The present invention pertains to a process for producing a vehicular pneumatic tire in which, in order to produce and apply a preferably unvulcanized tread strip to a partially completed tire which already has a cambered carcass and a ply packet radially outward therefrom, at least two strips of material, each consisting of a mixture of rubber and/or plastic, are applied to the partial tire, while at least one strip of material is wound in numerous essentially adjoining windings running in the circumferential direction of the tire.
A process for producing a vehicular pneumatic tire, in which a strip of rubber material is wound in numerous essentially adjoining windings around a partial tire, is known from the state of the art (e.g., R. A. Cronin: Elastomerics, August 1987, pages 2427). The advantages of this process lie specifically in the fact that only small extruders need to be made ready for the treadstrip mixtures.
Various demands are placed on the tread strip of a vehicular pneumatic tire. For instance, the part of the tread strip that has direct contact with the roadway must have optimal road grip. At the same time, resistance to wear, roll resistance and adequate grounding capability for electrostatic charges should be optimized. Heretofore, a single rubber mixture was used for the part of the tread strip that makes contact with the roadway. This rubber mixture must fulfill almost all demands. However, it is disadvantageous that each characteristic of the mixture coming into contact with the roadway can be varied only within certain limits so as not to negatively affect other characteristics.
In order to optimize still further the characteristics of the vehicular pneumatic tire, it is known that the tread strip can be made up of two parts of different mixture compositions running in the radial direction. Thus, part of the tread strip coming into contact with the roadway (cap) should already possess the characteristics cited above as to wear, adherence and resistance to roll. At the same time, the base rubber mixture directly beneath the cap rubber mixture should be optimized in such a way that, e.g., the resistance to roll is positively affected.
The production of such unvulcanized tire tread strips is usually accomplished with an extruder, the nozzle of which determines the pattern of the tread strip slug. However, it is not easily and uncomplicatedly possible, e.g., to provide different zones of the surface of the tread strip (e.g., shoulder area and midsection) coming into contact with the roadway with mixtures of different composition, e.g., in order to improve the traction of the tire still further. Specifically, complicated extruder nozzles would be required in order to divide the tread strip slug into appropriately different zones with different mixtures. Furthermore, in the customary process for building tires, in which the tread strip slug is designed as a complete component, there exists the problem that the two ends of the tread strip slug form an abutment point (splice) where they are joined together. This splice must be separately pretreated (coated with a naphtha solution) in order to ensure adequate adhesion of the two ends.
It is therefore a fundamental objective of the present invention is to make available a vehicular pneumatic tire, the tread strip of which has outstanding characteristics in driving operation and can, at the same time, also be produced in a simple and uncomplicated process.
The above and other objects can be achieved according to the invention, in that, in the case of two strips of material, these consist of different mixtures and, depending upon the desired characteristics of the tire, they are arranged simultaneously or sequentially on different areas in the inner or the radially outer zone of the space occupied by the finished tread strip.
In keeping with the invention, the process of the winding of a strip of material to form the tread strip can be modified in such a way that the totality of the tire characteristics can be considerably improved. For the production of such a vehicular pneumatic tire, two or more essentially flat strips of material (preferred ratio of width to thickness  greater than 7:1) of rubber and/or plastic are used. In principle, it is also possible to apply several adjoining strips of material in the longitudinal direction. The individual strips of material consist of a single mixture of rubber and/or plastic and are arranged on their respective zones in the tire. The mixture of rubber and/or plastic also contains, in addition to the respective polymers customarily used in the tire art (e.g., SBR, BR, NR), customary fillers (e.g., carbon black, silica), and additives (e.g., sulfur, accelerators, processing adjuvants).
In the winding of the material strips according to the invention, no splice results as in the case of the conventional tire building process. Since the strip of material is wound while warm and therefore has sufficient adhesiveness, the use of naphtha containing adhesion enhancers can be dispensed with.
It is especially advantageous when the radially inner part of the tread strip (base) and the part between the base and the surface (cap) coming into contact with the roadway is produced from at least two different strips of material. In this way it is possible that the strip of material forming the base layer can be first wound on completely. After the application of the base layer, there follows the winding on of the next strip of material which forms the cap. Ideally, however, the cap and the base are applied simultaneously. So it is possible that, e.g., beginning at an axial limit of the tire slug, the material strip of the base is first applied by winding and offset therefrom (offset, e.g., by one winding) e.g., a strip of material of the cap mixture is applied to the wound strip of material of the base mixture. Using such a procedure, the tire tread strip slug is completed especially in a timely fashion. In a conventional cap and base buildup, large extruder facilities with complicated nozzles were required in order to prepare such a vehicular pneumatic tire. It is also possible in keeping with the invention to undertake rapid and uncomplicated conversion to various mixtures in order to ensure optimal adaptation of the production, e.g., from summer to winter tires.
It is also advantageous when the radially inner part of the tread strip (base) and parts forming the surface of the tread strip coming into contact with the roadway are formed from a strip of material filled with a carbon black base mixture and that the remaining areas between the base and the surface coming into contact with the roadway are filled by winding on a second strip of material of a cap mixture or by inserting a single thick strip. The thickness of the zone occupied by the base mixture (in the radial direction) in certain zones of the tire and depending upon the dimension of the tire, is 2-5 mm and in other zones corresponds with the total thickness of the tread strip. The zones that do not have the full thickness of the tread strip are filled in by winding on a second strip of material or by inserting a single thick strip.
The winding on of a second strip of material, which consists of a cap mixture, can preferably be accomplished during the winding of the strip of base material, e.g., with a different rate of advance. The mixture of the second strip of material or the single strip preferably contains silica as a filler. The advantage of such a combination lies in the fact that running surface mixtures containing silica impart to the tire a slight resistance to roll and good skid characteristics on wet pavement although it does impart to the tread strip a low grounding capability due to its low electrical conductivity. With the combination mixture containing carbon black and silica according to the invention in the surface of the tread strip coming into contact with the roadway, the strip of material containing carbon black, which is itself in contact with conductive layers of the tire (e.g., the rubber coating of the bracing ply) ensures the grounding of electrostatic charges.
In this embodiment, it is highly desirable that the winding of the strip of material containing carbon black be accomplished in such a way that it is continuously in the surface coming into contact with the roadway. However, it is also possible in principle, by means of a suitable winding advance or by using a great number of strips of material with appropriate mixtures, to insert the mixture layer containing carbon black in drop form into the surface coming into contact with the roadway so that no encircling conductive band is formed. The xe2x80x9cgapsxe2x80x9d formed thereby are then filled in with the strip of material of the rubber mixture of the cap. In principle, it is also possible that two rubber mixtures containing carbon black form the material strip of the cap and base mixture. As already noted, it is here also advantageous when the strips of material are applied at the same time, since this facilitates a more rapid production of the vehicular pneumatic tire.
In an advantageous fashion, at least two strips of material of different mixtures can be wound onto the partial tire in such a way that the surface of the finished tire coming into contact with the roadway has alternating areas, which are formed from the respective individual mixtures of the strips of material. It is possible in that way, e.g., that in the finished tire raised areas of the pattern (ribs, bumps) have a very precise mixture composition, while the grooves or the edges of bumps of the pattern have a different composition. This makes it possible for the mixture composition of the tire to adapt better to roadway conditions.
It is especially advantageous when, in the finished tire, at least the two radially outer shoulder areas of the tread strip (e.g., cap and base part or only the cap part) each consist of a strip of material of a winter mixture. Then the traction of the tire, especially when manipulating curves, is optimized, so that an adaptation to the roadway conditions can ensue more readily. The shoulder area is the peripheral part of the tire, which maximally occupies 15% of the axial extension of the tread strip, related to the new tire, coming into contact with the roadway. Here it is again preferred that the entire radially outer zone of the tread strip, which comes into contact with the roadway, be made of a strip of material which imparts good winter driving characteristics to the tire in the vulcanized state.
It is especially advantageous when the areas forming the surface of the tread strip coming into contact with the roadway, in which tread patterns (fine incisions or grooves) are formed during the vulcanization, are formed from a strip of material with a higher electrical conductivity in the vulcanized state and, in the forming of the tread incisions, the mixture of this strip of material is brought into contact with another mixture, which also has a high electrical conductivity.
In the formation of the tread incisions, raised areas of the vulcanization form (lamellar strips of metal and lands) are pressed into the slug during the vulcanization process. Since, e.g., the strip of metal does not cut the mixture but merely displaces it, the mixture at the surface is carried radially inward by the strip of metal, and can there make contact with a conductive mixture, which is located radially inside the tire (e.g., the base mixture or the rubber coating of the bracing ply). The grounding of electrostatic charges can then ensue via a conductive mixture of crosslinked rubber and/or plastic. This mixture is found essentially only in the area of the lamellar edges or the edges of the tread bumps, yet coming into contact with the surface contacting the roadway. This strip of material, which is applied to the surface of the tread strip, preferably contains carbon black as a filler, so that it has sufficient conductivity. The rest of the surface coming into contact with the roadway preferably contains silica as a filler, since the positive characteristics already mentioned, such as reduced resistance to roll and good skid behavior on wet pavement, are positively influenced thereby. Advantageously, the material strip conductive in the vulcanized state is also wound on.
The process according to the invention can be used for producing recapped tires and new tires. Especially favored is the use of the process according to the invention, in which a partial tire is prepared in processing step A to the point that the air-impervious inner layer, one or more layers of the carcass, optionally the bead core or the additional layers reinforcing the bead area, one or more belted layers and optionally a single or multiple part binding band form the partial tire. According to the application, the belted layers and optionally the binding band and/or optionally other reinforcing layers are formed radially above the carcass and encompassing the term xe2x80x9cbelt reinforcement.xe2x80x9d It is furthermore possible that parts of the tread strip, e.g., a tread strip substrate and/or a tread strip base layer, be applied to the partial tire as the radially outermost layer. This partial tire (A) is essentially vulcanized completely.
The vulcanization process is preferably carried out in a vulcanization form, which makes it possible to impart to both the surface and the strength element(s) a predetermined crosssectional contour. In this manner a partial tire is obtained, which can be simply and uncomplicatedly completed in the subsequent process step B. This makes it possible to influence and achieve tire uniformity.
The essentially vulcanized partial tire can be stored for a longer period of time, so that the decision as to the manner in which the tire is to be completed (e.g., relative to the tread strip mixture or the profile of the tread strip) can be postponed to a later point in time. The tire manufacturer is then in a position to react appropriately and promptly to the demands of the market. The advantage of this process lies in the fact that with an essentially fully vulcanized partial tire without a profiled tread strip, e.g., the tread strip substrate or the tread strip base layer, rests against the inner wall of the heated form during vulcanization, so that due to inner pressure in the form, no displacements can be caused in the woven structure of the belted binding, as is occasionally observed in the common vulcanization of belt layers and the tread strip, on which profiled bumps must be pressed by inner pressure in the form.
The vulcanization steps A and B may also be distinguished in such a way that the partial tire is produced in processing step A by fabricating an air-impervious inner layer, a carcass containing strength elements, optionally belt cores and optionally rubber layers reinforcing the belt area and at least one belted layer and, in production step B, the partial tire is built into a complete tire by adding the unvulcanized single or multiple part binding band and the complete tread strip. The application of a single or multiple part binding band, which also consists of strength elements, usually textile e.g., nylon embedded in rubber, and the tread strip in processing step B has the advantage that in the finished tire a longitudinal tension uniformly distributed over the width of the tire is realized, which is influenced in the tire contour by variable tension application, by imparting a contour to the partial tire which varies from the contour imparted in processing step B, thus making it deliberately possible to optimize certain tire characteristics, such as wear or high speed capability.
Further design possibilities in respect to processing steps A and B and their advantages are set forth in DE 19,507,486 Al which is relied on and incorporated herein by reference.